1. Field of the Invention
This invention is a tool for preparing broken stud bolts or the like for extraction by screw extractors and more specifically is a guide for centering a center punch and/or a drill on a the broken face of a stud.
2. Background of the Invention
When a stud bolt bolts breaks off, it leaves, in the threaded bore, a threaded portion which must be removed prior to insertion of a new stud. Typically, the remaining portion is removed by drilling into the stud's broken face, by driving or screwing an extractor into the drilled hole to engage the stud remnant and, then, by turning the extractor to unscrew the remnant from the hole.
It is highly desirable that the hole be drilled axially for several reasons. First, drilling an off-center hole may damage the bore threads. Second, an axial hole helps prevent extractor breakage. An axial hole allows use of the largest possible drill, without damaging the threads, which, in turn, allows use of the largest possible extractor. Also, an extractor is less likely to be broken because less force needs to be applied to an extractor in an axial hole to provide the necessary extraction torque.
However, the typical rough and slanted broken face of a stud makes drilling an axial hole difficult.
Additionally, stud bolts break off in a variety of positions: far into the bore, in the bore near the orifice, at a threaded portion outside the bore, at a shank portion outside the bore or in the larger bore of an attached captive piece.
Therefore, it is desirable to have a tool for guiding of a center punch and/or drill into engagement with a stud's broken face regardless of the location of the break.